1. Field of the Invention
The invention pertains to a self-pumping hydropneumatic spring strut with internal level control, especially for motor vehicles, with a damping medium-filled working cylinder under the pressure of at least one gas cushion located in a high-pressure chamber and acting as a spring, the working cylinder being divided into two working spaces by a working piston carried by a hollow piston rod.
A piston pump, which is driven by the movements of the spring, conveys damping medium from a low-pressure chamber into the working space connected to the high-pressure chamber, the pump cylinder of the piston pump being formed by the hollow piston rod. A hollow pump rod, which is attached to the working cylinder and carries at its forward end a suction valve, travels in the bore of the hollow pump rod, which is connected with the low-pressure chamber with a control opening, which can be closed as a function of the position of the working piston in the working cylinder, and which connects the working space connected to the high-pressure chamber to a control channel, which is itself equipped with a throttle and which opens out into the low-pressure chamber.
A first channel extends from one of the working spaces to an adjustable damping valve, which is connected to the other working space and to the high-pressure chamber by way of a second channel.
2. Description of the Related Art
U.S. Pat. No. 4,993,693 discloses a spring strut having an internal level control system which uses a piston pump to convey damping medium from a low-pressure chamber into the working space connected to the high-pressure chamber. This spring strut is also provided with an adjustable damping valve, which controls the damping force and is continuously variable during operation of the vehicle.